1. Technical Field
The invention relates to an image processing technique of performing color conversion processing on an input image.
2. Related Art
Color conversion processing is performed on an image in various situations such as a situation that image processing is performed on a scanned-in image and a resulting processed image is output to a print engine in a copier. Among conventional color conversion methods in copiers, a method, which uses a multi-dimensional look-up table with interpolation, is called “DLUT” (direct look-up table).
FIG. 9 illustrates an exemplary color conversion method using a DLUT. In this example, the three-dimensional L*a*b* color space is divided in such a manner that each of the L*, a*, and b* axes is divided into a prescribed number of sections. The space is divided into cubes or rectangular parallelepipeds and their vertexes are called “lattice points.” Color conversion result values are held for the respective vertexes. In the case of a conversion into the CMYK color space, for example, CMYK values are held so as to correspond to the respective lattice points.
For interpolation operation, each divisional cube or rectangular parallelepiped is further divided into six tetrahedrons as shown in FIG. 9. To which tetrahedron input values (L*, a*, b*) belong are judged on the basis of the input values (L*, a*, b*) themselves, and an interpolation operation is performed by using CMYK values corresponding to the four vertexes (lattice points) of the tetrahedron thus found. In this manner, arbitrary input values (L*, a*, b*) can be converted into CMYK values.